Neutrophils plug capillaries in acute experimental retinal ischemia

Capillary plugging by neutrophils appears to be the mechanism responsible for the no reflow phenomenon following experimental ischemia in many tissues. The purpose of this study was to determine if neutrophils plug capillaries in experimental retinal ischemia. Unilateral retinal ischemia was produced in albino rats by focally exposing three adjacent retinal arterioles to argon blue-green laser light at 100 mW. Total occlusion was achieved in at least two vessels in each eye. The animals were euthanized at 3, 6, 8, or 24 hr following laser treatment. Nonlasered eyes of 17 animals served as controls. Trypsin digests were prepared of the retinal vasculature following formalin fixation. The total number of neutrophils present in the capillaries of each retina was counted using a light microscope and expressed as the number of cells per retina. Other eyes were fixed in glutaraldehyde:paraformaldehyde and the retinal tissue prepared for light and electron microscopy. The mean number of neutrophils in capillaries of retinas subjected to laser treatment was significantly higher than that in untreated control retinas at all time periods studied and increased with time from 3 to 6 hr. Intact as well as degranulated PMNs were present in the capillaries. The presence of large numbers of neutrophils plugging capillaries and their increased number with duration of ischemia supports the hypothesis that they contribute to capillary nonperfusion following acute retinal ischemia.